Inducing of dominant polar forms in poly(vinylidene fluoride) with super toughness by adding alkyl ammonium salt

Polar β and γ crystalline forms, especially the β form, are of great importance to the piezoelectric/ferroelectric property of poly(vinylidene fluoride) (PVDF). Dominant polar crystal forms (containing both β and γ forms) are induced in PVDF by simply adding a small amount of dioctadecyl dimethyl ammonium chloride (DDAC, a kind of alkyl ammonium salt used to treat clay). By comparing with the PVDF/clay and PVDF/DDAC modified-clay systems, it is demonstrated that it is DDAC that induces polar β and γ forms of PVDF rather than organoclay itself. The widely accepted mechanism that crystal lattice matching between PVDF and clay induces β form in PVDF/organoclay composite might be wrong. It is also interesting to find that super tensile toughness can be achieved by adding a small amount of DDAC. These new findings are very important for the understanding of the formation mechanism of polar forms of PVDF and its application.